In the drilling of oil and gas wells, it is frequently necessary and/or desirable to transmit electrical power and/or signals from surface controls, measuring and/or recording devices to sensing or other electrical devices located in the lower portions or bottoms of boreholes. Usually, this communication is accomplished by lowering an insulated cable, with attached sensor or other device, through the drill string to the depth where the desired measurement or function is to be performed. This method necessitates discontinuance of the drilling operation, is time consuming and hence wastes expensive drilling time.
Ideally, the sensing or downhole device is prepositioned in the drill string, possibly in the lowest length of drill pipe or drill collar just above the drill bit with electrical communication to the surface being through a conductor system that is an integral part of each drill stem section. This concept is old and well known as illustrated by the expired patent to Polk, No. 2,000,716, which proposes an insulated coaxial inner conductor and uses the drill string as the outer electrical conductor of the system. Detachable insulated helical springs are used as connectors between adjacent sections of the inner conductor. However, Polk and other proposed system involve the engagement of coaxial insulated parts which are subject to irreparable damage under the rough handling associated with the coupling and uncoupling of drill pipe in well drilling operations. Furthermore, none of these systems provides a satisfactory method of mechanically securing the inner conductor and insulation in the drill stem so as to prevent dislocation under the rigors of well drilling.
Also, no means is provided to accommodate abrupt changes in the inner diameter of drill stem sections commonly located at the juncture of the drill pipe and its welded-on tool joints or coupling collars. If these diameter discontinuities are not remedied, the extreme fluid pressures encountered in deep well drilling can easily rupture both the inner conductor and its insulating material and thereby cause an electrical failure. These systems also fail to provide pressure seals at the tool joints which are adequate to prevent high pressure fluid from migration into the conductor-insulator interfaces causing high electrical leakage and possible separation of the inner conductor and its insulating sleeve from the drill pipe wall.
The faults of these previously conceived systems are overcome by a new conductor design and fabrication method as presented in this invention and provides all the following attributes of a viable, efficient electrical system:
1. Economical fabrication;
2. Installation in unmodified standard drill pipe;
3. Two-way electrical signal and/or power transmission;
4. High immunity to electrical noise, external or associated with the drilling operation;
5. Sufficient high speed signal and/or power transmission to permit duplex or multiplex operation of more than one signal or power circuit;
6. Applicability to any metallic pipe system incorporating mechanically connectable sections;
7. Negligible resistance to fluid flow in the pipe or drill stem;
8. Convenient means of electrical connection to both surface and to the drill stem instrumentation; and
9. Capable of a slip-ring tubing connection between the drill kelly and top rotary joint so as to permit downhole monitoring or control while drilling.